Many industries such as chemical manufacturing, power generation, mining, the oil industry, along with numerous others, have occasion to suspend solid particles in some type of fluid. For example, a high fuel-value coal-water suspension (or slurry) that can be injected directly into a furnace as a combustible fuel can be used to replace large quantities of fuel oil. Generally, it is highly desirable that the production time, expense, and amounts of carrier solvents and additives of such suspensions (or slurries) be minimized as much as possible.
Often, for efficient practical use, the suspension must have several essential characteristics. It must have long-term static stability so that it can be stored for extended periods of time by suppliers or at the point of use. During such storage, the slurry must remain uniformly dispersed or, at most, be subject to some soft subsidence which can be easily redispersed by stirring.
With respect to solid fuels used for processes such as power generation or chemical processing, uniform solid dispersion is essential for a reliable fuel source. Such processes can require various concentrations of the solid fuel in a liquid medium (e.g. a slurry). The liquid medium can be any suitable liquid carrier that is beneficial for the specific process. Requirements and process optimization can require varying concentrations of the solid material in the liquid carrier. Thus, in certain applications, reducing the liquid portion of the suspension is desired. However, the suspension must also be sufficiently fluid; that is, have a sufficiently low viscosity, to be pumped to and distributed into the next processing stage.
In order to increase the solids concentration of a suspension, the skilled artisan may use a dispersant such as pH modifiers and the sulfonate salts of ligands, naphthalenes, polystyrenes, polymethacrylates and polyolefins or other suitable dispersants. Such modifiers not only allow for increased solid concentration, but also serve to reduce viscosity. However, when using such modifiers, it is useful and often necessary to determine the optimal type and amount of modifier to achieve the desired effect. For example, if too much modifier is used, the suspension can become unstable and the solids can separate from the liquid.
Various methods have been developed to measure the rates at which particles settle out of suspension. Some of these methods involved visually observing the rates at which the particles settled to the bottom of the container or using some type of detector to measure the settling of the particles. These methods often did not work well when the fluid was opaque or there were large numbers of fine particles that made visual observation or measurement with some type of light detector impractical.
The present invention addresses the above problems by enabling the user to determine the settling rates of solids in a suspension (e.g., a slurry). The present invention also enables the user to determine whether, and how much, modifier should be used. Moreover, the system and method of the present invention does not hamper the ability to observe or measure the rate of particle settling visually or optically. While the examples show the present invention in relation to coal slurries, the invention would be equally useful to other applications involving the suspension of particles in a liquid.